The present invention relates to a pulse forming circuit with delayed pulse width control and in particular to a circuit wherein the change in pulse width lags the change in pulse amplitude so as to produce muted brass voices in electronic organs.
It has been established that the tonal quality of a note from a musical instrument is dependent upon the harmonic content of the wave form of the note. Brass instruments, in particular, contain harmonics in nearly equal portions, that is, the amplitude of the harmonics of a note from a brass instrument do not fall off sharply in amplitude with increasing frequency. A square wave with narrow pulse width has a harmonic structure whereby the amplitudes of the harmonics are approximately equal so that the tone is very bright and is a suitable wave form for producing brass voices. A wider pulse possesses a decrease in amplitude for increasingly higher harmonics relative to the amplitude of the fundamental and the tone is more mellow than that of the narrow pulse.
When a key in an electronic organ is depressed, the sound of a brass instrument to be synthesized should build in amplitude and harmonic structure but, to closely copy an actual brass instrument in which the player may change the tonal quality by changing lip pressure, the tonal quality of the sound may lag slightly the initial increase of amplitude. This effect is most pronounced when a mute is used with a trumpet or trombone wherein the mute is removed after wind pressure is applied to the horn and thus a mellow sound is first heard and then a brighter sound follows.